| Scheduler |
| ========= |
| |
| Scheduler's job is to maintain the list of tasks and decide which one |
| should be running next. |
| |
| Description |
| ------------- |
| |
| Task states can be *running*, *ready to run* or *sleeping*. |
| |
| When task is *running*, CPU is executing in that task's context. The |
| program counter (PC) is pointing to instructions task wants to execute |
| and stack pointer (SP) is pointing to task's stack. |
| |
| Task which is *ready to run* wants to get on the CPU to do its work. |
| |
| Task which is *sleeping* has no more work to do. It's waiting for |
| someone else to wake it up. |
| |
| Scheduler algorithm is simple: from among the tasks which are ready to |
| run, pick the the one with highest priority (lowest numeric value in |
| task's :c:member:`t_prio` field), and make its state *running*. |
| |
| Tasks which are either *running* or *ready to run* are kept in linked |
| list ``g_os_run_list``. This list is ordered by priority. |
| |
| Tasks which are *sleeping* are kept in linked list ``g_os_sleep_list``. |
| |
| Scheduler has a CPU architecture specific component; this code is |
| responsible for swapping in the task which should be *running*. This |
| process is called context switch. During context switching the state of |
| the CPU (e.g. registers) for the currently *running* task is stored and |
| the new task is swapped in. |
| |
| API |
| ---- |
| |
| .. doxygengroup:: OSSched |
| :content-only: |
| :members: |
